A simple benchmark of FPU math functions using RDTSC.

math_bench.c

/*
    James William Fletcher (github.com/mrbid)
        August 2021

    Simple math function benchmark using RDTSC.
    https://james-william-fletcher.medium.com/rdtsc-the-only-way-to-benchmark-fc84562ef734
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <locale.h>
#include <sys/time.h>
#include <x86intrin.h>

#define AVGITER 3000000

static inline float rsqrtss(float f) // this is not a fair comparison to sqrt(double)
{
    return _mm_cvtss_f32(_mm_rsqrt_ss(_mm_set_ss(f)));
}

int main()
{
    setlocale(LC_NUMERIC, "");
    float ret = 0;
    uint64_t st = 0, et = 0, avg = 0;

    // cbrt
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += cbrt(st);
        avg += __rdtsc()-st;
    }
    printf("cbrt() Cycles: %'lu\n", avg / AVGITER);

    // exp10
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += exp10(st);
        avg += __rdtsc()-st;
    }
    printf("exp10() Cycles: %'lu\n", avg / AVGITER);

    // exp2
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += exp2(st);
        avg += __rdtsc()-st;
    }
    printf("exp2() Cycles: %'lu\n", avg / AVGITER);

    // exp
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += exp(st);
        avg += __rdtsc()-st;
    }
    printf("exp() Cycles: %'lu\n", avg / AVGITER);

    // hypot
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += hypot(st, st);
        avg += __rdtsc()-st;
    }
    printf("hypot() Cycles: %'lu\n", avg / AVGITER);

    // log10
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += log10(st);
        avg += __rdtsc()-st;
    }
    printf("log10() Cycles: %'lu\n", avg / AVGITER);

    // log2
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += log2(st);
        avg += __rdtsc()-st;
    }
    printf("log2() Cycles: %'lu\n", avg / AVGITER);

    // log
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += log(st);
        avg += __rdtsc()-st;
    }
    printf("log() Cycles: %'lu\n", avg / AVGITER);

    // pow
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += pow(st, st);
        avg += __rdtsc()-st;
    }
    printf("pow() Cycles: %'lu\n", avg / AVGITER);

    // sqrt
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += sqrt(st);
        avg += __rdtsc()-st;
    }
    printf("sqrt() Cycles: %'lu\n", avg / AVGITER);

    // rsqrtss
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += rsqrtss(st);
        avg += __rdtsc()-st;
    }
    printf("rsqrtss() Cycles: %'lu\n", avg / AVGITER);

    // acos
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += acos(st);
        avg += __rdtsc()-st;
    }
    printf("acos() Cycles: %'lu\n", avg / AVGITER);

    // asin
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += asin(st);
        avg += __rdtsc()-st;
    }
    printf("asin() Cycles: %'lu\n", avg / AVGITER);

    // atan
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += atan(st);
        avg += __rdtsc()-st;
    }
    printf("atan() Cycles: %'lu\n", avg / AVGITER);

    // atan2
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += atan2(st, st);
        avg += __rdtsc()-st;
    }
    printf("atan2() Cycles: %'lu\n", avg / AVGITER);

    // cos
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += cos(st);
        avg += __rdtsc()-st;
    }
    printf("cos() Cycles: %'lu\n", avg / AVGITER);

    // tan
    avg = 0;
    for(int i = 0; i < AVGITER; i++)
    {
        st = __rdtsc();
        ret += tan(st);
        avg += __rdtsc()-st;
    }
    printf("tan() Cycles: %'lu\n", avg / AVGITER);
    
    // done
    printf("\n%c\n", (char)ret);  // forces the compiler to not disregard the functions we are testing
    return 0;
}

cbrt() Cycles: 31
exp10() Cycles: 19
exp2() Cycles: 17
exp() Cycles: 17
hypot() Cycles: 16
log10() Cycles: 22
log2() Cycles: 21
log() Cycles: 18
pow() Cycles: 32
sqrt() Cycles: 18
rsqrtss() Cycles: 18
acos() Cycles: 20
asin() Cycles: 21
atan() Cycles: 24
atan2() Cycles: 34
cos() Cycles: 168
tan() Cycles: 205